The present invention relates to a suction apparatus for an engine, which can reduce noise based on suction noise in an engine room.
Conventionally, in order to reduce engine noise, a technique disclosed in Japanese Patent Laid-Open No. 60-22021 is known. In the technique described in this prior art, a suction path is connected to resonance chambers via tubular communication members, and the resonance chambers are coupled to each other via a coupling pipe in which a switching valve is inserted. The switching valve is switching-controlled in accordance with an engine speed, thereby reducing a noise level.
However, as described above, in the prior art arrangement in which a silencer is directly connected to the suction path to reduce noise of an air intake system, a large silencer is required. For this reason, when a space around an engine is narrow, it is difficult to arrange the silencer.
More specifically, the suction path in which a throttle valve is inserted has a relatively large path area, and the resonance chamber for attenuating a pressure vibration in this portion inevitably becomes large. In recent years, an engine room is confined, and the position of an air cleaner is limited. As a result, in some existing engines, the length of the suction path must be set to undesirably increase suction noise since the noise is tuned to the frequency of a pressure vibration applied from a suction port to the suction path at an idling engine speed in consideration of pressure-vibration characteristics of the suction path at the upstream side of a throttle body. In these engines, suction noise becomes conspicuous in an idling state in which the noise level of the entire engine is lowered. For this reason, a demand has arisen for a compact silencer structure which can reduce suction noise which is tuned in the idling state.